1. Field of the Invention
The present invention relates to a lip type seal which is used as a seal for a reciprocating part of a fuel pump in a fuel injection pump for a gasoline direct injection type engine and is used in the other general oil, pneumatic and hydraulic pressure devices.
2. Description of the Conventional Art
The gasoline direct injection type engine is structured such as to directly inject fuel having a high pressure into a cylinder so as to burn for the purpose of regulating exhaust gas and improving fuel consumption in recent years, and in accordance with higher performance of a fuel injection pump used for directly injecting fuel having the high pressure, there is a tendency that the environment near a seal used in the fuel injection pump becomes more and more severe.
Conventionally, as a seal used in the fuel injection pump, there has been known an oil seal made of a rubber-like elastic material and integrally provided with a first seal lip to seal a high-pressure gasoline or the like, which is a first sealed fluid, at a first sealed fluid side, and a second seal lip to seal an oil for cooling and lubrication existing at a second sealed fluid side opposite in an axial direction to the first sealed fluid side (refer to Japanese Unexamined Patent Publication No. 8-68370). However, since the material is constituted by the rubber-like elastic material, a pressure resistance is short due to the high pressure of the first sealed fluid, and a chemical resistance against an inferior fuel is poor, so that there is a risk that the seal function thereof can not be sufficiently satisfied. Accordingly, a lip type seal using resin such as PTFE or the like which is excellent in the pressure resistance and the chemical resistance has been widely used.
A conventional lip type seal 101 is provided with a seal main body 107 having an approximately cylindrical concave portion 102 which is open to a first sealed fluid side A, a first inner peripheral seal lip 103 and a first outer peripheral seal lip 104 which are provided in inner and outer peripheries of the cylindrical concave portion 102 and slidably contact with a shaft and a housing, an approximately wedge-shaped concave portion 105 which is open so as to face to the shaft at a second sealed fluid side B, and a plate-shaped second inner peripheral seal lip 106 formed at a second sealed fluid side B of the wedge-shaped concave portion 105, and being integrally formed by resin, and an elastic body 111 inward installed in the cylindrical concave portion 102, as shown in FIG. 3. The second inner peripheral seal lip 106 is greatly bent around a point of a bottom end point M of the wedge-shaped concave portion 105 in a direction of an arrow Y as shown by a one-dot chain line at a time of inserting the shaft 108 to the inner peripheral side from the first sealed fluid side A toward the second sealed fluid side B (in a direction of a thick arrow X), as shown in FIG. 4, and fastening is secured by reaction force to restore its original state. However, since the seal main body 107 is formed by resin, the second inner peripheral seal lip 106 has a problem that its seal performance is lowered by reduction in the fastening caused by a creep. Further, since the second inner peripheral seal lip 106 is bent around point M so as to seal on the basis of its reaction force, there is a risk that stress is concentrated on the point M and durability is lowered. Further, since the second inner peripheral seal lip 106 is greatly bent, settlement of the seal main body 107 is not stabilized at a time of being installed to an annular gap. Therefore, it is necessary to form an outer peripheral collar portion 109 on the seal main body 107 and there is a problem that a manufacturing cost becomes high.